US EPA

1568316 

Journal Article 

Mechanisms for the Reaction of Thiophene and Methylthiophene with Singlet and Triplet Molecular Oxygen 

Song, X; Fanelli, MG; Cook, JM; Bai, F; Parish, CA 

2012 

1 

Journal of Physical Chemistry A
ISSN: 1089-5639
EISSN: 1520-5215 

116 

20 

4934-4946 

22515263 

10.1021/jp301919g 

WOS:000304338600014 

Mechanisms for the reaction of thiophene and 2 methylthiophene with molecular oxygen on both the triplet and singlet potential energy surfaces
(PESs) have been investigated using ab initio methods. Geometries of various stationary points
involved in the complex reaction routes are optimized at the MP2/6-311++G(d, p) level. The
barriers and energies of reaction for all product channels were refined using single-point
calculations at the G4MP2 level of theory. For thiophene, CCSD(T) single point energies were also
determined for comparison with the G4MP2 energies. Thiophene and 2-methylthiophene were shown to
react with 02 via two types of mechanisms, namely, direct hydrogen abstraction and
addition/elimination. The barriers for reaction with triplet oxygen are all significantly large
(i.e., >30 kcal mol(-1)), indicating that the direct oxidation of thiophene by ground state
oxygen might be important only in high temperature processes. Reaction of thiophene with singlet
oxygen via a 2 + 4 cycloaddition leading to endoperoxides is the most favorable channel.
Moreover, it was found that alkylation of the thiophene ring (i.e., methyl-substituted thiophene)
is capable of lowering the barrier height for the addition pathway. The implication of the
current theoretical results may shed new light on the initiation mechanisms for combustion of
asphaltenes.